Computational insight into the effect of CaO/MgO Substitution on the Structural Properties of Phospho-Silicate Bioactive Glasses.

The effect of the replacement of CaO for MgO on the structural properties of the 45S5 Bioglass with composition 46.2SiO2\ub724.3Na2O\ub7(26.9 12 x)CaO\ub72.6P2O5\ub7xMgO where x = 0, 5, 10, 15, 20, and 26.9 mol has been studied by means of molecular dynamics simulations. The results confirmed the complexity of the local environment of Mg ions which are coordinated by 5 nonbridging oxygens of different TO4 tetrahedra (T = Si/P) leading to large rings in the structures. A rough correlation between the average dimension of the rings found in the structure and the computed Young\u2019s modulus is obtained. The Young\u2019s modulus decrease at low Mg-content reaching a minimum for the 46.2SiO2\ub724.3Na2O\ub716.9CaO\ub72.6P2O5\ub710MgO glass. At this composition, Mg is homogeneously distributed in the silica rich region together with Ca and Na ions but is almost totally absent from the Ca 12Na-phosphate rich regions. The results suggest that the ideal glass composition for lowering the Young\u2019s modulus preserving a specific bioactivity can be found below 10% of MgO content